On March 24, local time, Oklahoma Governor Kevin Stitt appointed energy executive Alan Armstrong to the U.S. Senate to serve until the end of the year. Armstrong will fill the vacancy left by Markwayne Mullin, a Republican, who has become the new Secretary of Homeland Security. According to Jin10, Governor Stitt had previously promised to select a "conservative" to fill Mullin's seat. Under Oklahoma law, Armstrong must pledge not to run in the official term election scheduled for this fall. Meanwhile, Republican U.S. Representative Kevin Hart quickly announced his candidacy for the Senate seat and has received endorsement support from U.S. President Donald Trump.